Sparrowhawk

The Eurasian (or Northern) Sparrowhawk (Accipiter nisus) is a small bird of prey in the family Accipitridae. Adult male Eurasian Sparrowhawks have bluish grey upperparts and orange-barred underparts; females and juveniles are brown above with brown barring below.

Sparrowhawk

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The female is up to 25% larger than the male – one of the largest differences between the sexes in any bird species. Though it is a predator which specialises in catching woodland birds, the Eurasian Sparrowhawk can be found in any habitat and often hunts garden birds in towns and cities. Males tend to take smaller birds, including tits, finches, and sparrows; females catch primarily thrushes and starlings, but are capable of killing birds weighing 500 grams (18 oz) or more.

The Eurasian Sparrowhawk is found throughout the temperate and subtropical parts of the Old World; while birds from the northern parts of the range migrate south for winter, their southern counterparts remain resident or make dispersive movements. Eurasian Sparrowhawks breed in suitable woodland of any type, with the nest, measuring up to 60 cm (2.0 ft) across, built using twigs in a tree. Four or five pale blue, brown-spotted eggs are laid; the success of the breeding attempt is dependent on the female maintaining a high weight while the male brings her food. The chicks hatch after 33 days and fledge after 24 to 28 days.

The Eurasian Sparrowhawk is a small bird of prey with short, broad wings and a long tail, both adaptations to manoeuvring through trees. Females can be up to 25% larger than males and weigh up to twice as much. When females are larger than males, it is known as reverse sexual dimorphism; this is unusual in higher vertebrates but typical in birds of prey, and most marked in birds of prey which hunt birds.

The Eurasian Sparrowhawk’s pale underparts and darker upperparts are an example of countershading, which helps to break up the bird’s outline. Countershading is exhibited by birds of prey which hunt birds and other fast-moving animals. The horizontal barring seen on adult Eurasian Sparrowhawks is typical of woodland-dwelling predatory birds, while the adult male’s bluish colour is also seen in other bird-eating raptors, including the Peregrine Falcon, the Merlin and other Accipiters.

A study, using stuffed bird models, found that small birds are less likely to approach Common Cuckoos (a brood parasite) which have barred underparts like the Eurasian Sparrowhawk. Eurasian Reed Warblers were found to be more aggressive to cuckoos which looked less hawk-like, meaning that the resemblance to the hawk helps the cuckoo to access the nests of potential hosts.

A widespread species throughout the temperate and subtropical parts of the Old World, the Eurasian Sparrowhawk is resident or breeds in an estimated global range of 23,600,000 km2 (9,100,000 miles2) and had an estimated population of 1.5 million birds in 2009. Although global population trends have not been analysed, numbers seem to be stable, so it has been classified as being of Least Concern by IUCN. The race granti, with 100 pairs resident on Madeira and 200 pairs on the Canary Islands, is threatened by loss of habitat, egg-collecting and illegal hunting, and is listed on Annex I of the European Commission Birds Directive. It is one of the most common birds of prey in Europe, along with the Common Kestrel and Common Buzzard. The Norwegian and Albanian populations are declining and, in many parts of Europe, Eurasian Sparrowhawks are still shot. However, this low-level persecution has not affected the populations badly. In the UK, the population increased by 108% between 1970–2005, but saw a 1% decline over 1994–2006. In Ireland it is the commonest bird of prey, breeding even near the city centre of Dublin.

This species is common in most woodland types in its range and also in more open country with scattered trees. Eurasian Sparrowhawks prefer to hunt woodland edges, but migrant birds can be seen in any habitat. The increased proportion of medium-aged stands of trees created by modern forestry techniques have benefited the species, according to a Norwegian study. Unlike its larger relative the Northern Goshawk, it can be seen in gardens and in urban areas and will even breed in city parks.

Eurasian Sparrowhawks from colder regions of northern Europe and Asia migrate south for the winter, some to north Africa (some as far as equatorial east Africa) and India; members of the southern populations are resident or disperse. Juveniles begin their migration earlier than adults and juvenile females move before juvenile males. Analysis of ringing data collected at Heligoland, Germany, found that males move further and more often than females; of migrating birds ringed at Kaliningrad, Russia, the average distance moved before recovery (when the ring is read and the bird’s whereabouts reported subsequently) was 1,328 km (825 mi) for males and 927 km (576 mi) for females.